Drill bits are formed on a drill bit body or a set of cones which rotate in the drill bit during drilling. There are two types of tooth constructions that are prevalent today. In one instance, the teeth are fabricated from a unitary piece of metal so that the teeth are part of the drill bit body or cone. In another approach, the cone or bit body is drilled with a number of holes and teeth are inserted. In the latter instance, a harder tooth can be used. Indeed, it is possible to make inserts which mount in the formed holes in the drill bit body, the teeth being formed of much harder materials such as tungsten carbide. That is an extremely hard material. Even so, the insert tends to wear. The insert is normally protected by placing a synthetic diamond layer over the end of the insert. The synthetic diamond is sometimes known as a polycrystalline diamond compact and carries the abbreviation of PDC. In this regard, the PDC layer extends the life of the insert markedly.
The present disclosure is directed to an insert which is an elongate cylindrical body in the preferred embodiment, suitably sized and shaped, so that it fits in a hole formed in the drill bit body or some part of the bit body, and is equipped with a PDC crown or cap attached to the end of it. Such devices have been made heretofore. The present disclosure however sets forth a PDC protected insert which is ideally constructed for use in a drag bit. By way of background, some bits operate so that the teeth of the drill bit (of whatever construction) cut material by rolling so that the tooth is rolled into contact against the face of the partly finished borehole, and there are others that move the drill bit teeth across the face in a dragging motion. The roller bit construction involves a rotational movement of some part of the drill bit so that the tooth is loaded and rolls under load. This causes a crushing motion. By contrast, the tooth in a drill bit which drags across the working face operates in a different fashion. Loosely, it cuts a groove by chiseling or gouging the working face. This involves a sliding motion or a transverse motion across the face of the well borehole. Thus, the dragging motion creates a different kind of drilling motion in contrast with the rolling motion mentioned above.
The present disclosure is directed to a drag bit insert and to a drag bit insert which is constructed in a way so that the drag bit teeth last much longer. To last longer, the drag bit is equipped with teeth having the PDC crown formed on the end of the insert. Moreover, the end of the PDC insert is preferably circular so that the insert is covered completely at the end. When this is done, the covered portion of the insert is exposed to abrasion and tends to wear away. The insert body is constructed with a crown over a circular end face to assure a specified thickness of PDC material on the end of the insert. In addition to that, the insert (before the PDC layer is attached) is provided with two chamfered faces. The chamfered faces are located on opposite sides of the insert body. The tapered and chamfered faces enable the PDC material to provide an enhanced region of PDC material on the insert, thereby extending the life even when subject to losses of material due to abrasion. More particularly, the drag bit insert is installed so that the PDC crown on the end of the insert cylindrical body is joined to a larger surface area. So to speak, the insert body has a uniform conic face joined to the PDC crown except at the upstream and downstream sides of the insert body. Those are enhanced.
The present disclosure enhances performance of the insert, typically made of tungsten carbide by the incorporation of two chamfered faces which are ideally arranged 180.degree. spacing around the body. The two or more chamfered faces are cut at an angle in the range of about 15.degree. to about 45.degree. with respect to the centerline axis of the insert body. The two insert chamfers thereby extend the PDC contact region. The chamfered areas form a longer skirt or face at which abrasion occurs.
Summarizing the present invention, it preferably comprises a right cylinder construction insert preferably formed of hard metal. While other hard materials can be used, an enhanced version of the equipment incorporates a tungsten carbide insert body. The tungsten carbide body is shaped with a pair of spaced. chamfered surface areas. These define chamfered areas which are approximately planar, which extend at an angle of about 15.degree.-45.degree. with respect to the center axis of the insert body, and which extend to a greater length along the sides so that the PDC interface with the insert body is much greater. This improves fastening of the PDC crown to the insert body and lowers heat buildup during drilling or other cutting and abrasive applications.